Method of coating metallic material onto a metallic substrate

ABSTRACT

A method for coating surfaces portions of a metal workpiece with a different metal whereby the work-piece is immersed in a fluidized bed in which metal particles are suspended by an ascending gas current, inductively heated in the bed to cause deposition of the inductively heated regions and then inductively reheated outside the fluidized bed after deposition.

United States Patent Reinke et a1. 1 1 Dec. 9, 1975 METHOD OF COATING METALLIC 3.020,210 2/1962 Stephens et a1 1 17/010. 6 ERI L O A METALLIC 303L769 5/1962 Wilson 1 1 1 1 w I l7/DlG1 6 3,032,816 5/1962 Zimmerli 1l7/D1G16 SUBSTRATE 1053,704 9/1962 Munday 1 1 1 1 1 H ll7/D1G. 6 [75] Inventors: Friedhelm Reinke, Remscheid; 3,060,304 10/1962 Tanaka 11 117/1310. 6 Edgar Slengel, 1118 773 H1964 Bennett et a1, 117/D1G. 6 wuppertaLHahnerberg; Friedhelm gaun i v 1 emmer.... g Huckeswagen a of 3,282,249 1 H1966 Ramsay 1 1 17/21 X emany 3,383,233 5/1968 (7111616 4 117/21 x [73] Assignee: AEG-Elotherm G.m.b.H., 31419.40) 12/1968 Dettling 1 1 1 1 1 1 1 1 117/21 R h i LH t Germany 3.666253 5/1972 YOShlO et al 1 17/1310. 6

[221 Filed: Sept 1972 Primary Examiner-William D. Martin [21] A N 290,384 Assistant Examiner-5hrive P, Beck Attorney, Agent, or Firm-Cushman. Darby & Cushman [30] Foreign Application Priority Data Sept. 30, 1971 Germany 2148779 57 ABSTRACT {52] Us Cl 427/46 427/185 427H90 A method for coating surfaces portions of a metal [51] E: 305i) 3/02. b U24 workpiece with a different metal whereby the work- [58] Field of DIG6 93 2 31 piece is immersed in a fluidized bed in which metal 7/22: 5 d particles are suspended by an ascending gas current, inductively heated in the bed to cause deposition of [56} Reierences Cited the inductively heated regions and then inductively re- UNITED STATES PATENTS 7/1958 Gemmer l17/D1G. 6

heated outside the fluidized bed after deposition.

8 Claims, 3 Drawing Figures US. Patent Dec. 9, 1975 Sheet 1 of2 3,925,570

U.S. Patent Dec. 9, 1975 Sheet 2 of2 3,925,570

Ewan M METHOD OF COATING METALLIC MATERIAL ONTO A METALLIC SUBSTRATE The invention relates to the application of a coating of metallic material to prescribed surface areas, particularly of a metal workpiece.

For many technical applications, workpieces are needed in which portions of the workpiece surface, for instance an as yet unfinished metal part selected be cause of its mechanical strength, are coated with a different metallic material to provide, for instance, special hardness or resistance to wear. Both metallic materials may be metals, alloys or intermetallic compounds. It is frequently important that the two materials form an intimate bond at their contacting surfaces.

One way of applying a metallic coating to a metallic base material of different kind of metal is by spraying. Usually the coating material is sprayed in the form of fine droplets by means of a gas or plasma flame. However, experience has shown that in such metal spraying procedures the bond between the coating material and the base material is often rather poor. Moreover, in these processes it is difficult to produce coatings of uniform thickness. This is particularly true when surfaces of complex geometry are to be coated. Furthermore, when it is desired to provide a coating on concave surfaces it is often difficult and sometimes impossible for the sprayed material to reach some surface areas.

It is the object of the present invention to provide a method, and apparatus for performing the method of applying a coating of metallic material to specific surface areas of a base in such a way that an intimate bond is formed between the coating and the base material and a coat of uniform thickness is produced even when the surface configuration of the base material is complex.

According to the invention this is achieved by the method proposed by the present invention which consists in immersing at least the surface regions of the workpiece that are to be coated in a fluidized bed in which the material that is to be applied is maintained in powder form in a fluidized state by an ascending current of gas, and in inductively heating in the fluidized bed a surface layer of the workpiece in the regions that are to be coated. Preferably the fluidizing gas may be an inert gas and particularly a noble gas, such as Argon.

In a preferred feature of the method according to this invention a surface layer of regions to which the powder has been applied in the fluidized bed is again inductively heated outside the fluidized bed. The renewed inductive heating outside the fluidized bed may be carried out in the fluidizing gas used for maintaining the fluidized bed.

According to another feature of the invention the workpiece surfaces that are to be coated inside the fluidized bed are traversed past an inductive energy transducer. After the powder has been applied in the fluidized bed the surface regions that are to be coated may with advantage again traverse an inductive energy transducer outside the fluidized bed.

In a useful modification of the invention an inductive transducer which has effected the application of the powder inside the fluidized bed may be withdrawable from the fluidized bed at the same time as the workpiece to subject the surface regions that are to be coated to reheating. Finally yet another modification of the proposed method comprises repeating the sequence of treating steps at least once for the purpose of producing coatings of greater thickness.

For performing the method, apparatus according to the invention preferably includes a tank having with a perforated bottom for receiving the coating material in powder form, means for generating an ascending current of fluidizing gas in the tank, holding means for holding the workpiece in a position in which it is at least partly immersed in the fluidized bed and an inductor located in heating position in relation to the surfaces of the workpiece that are to be coated in the fluidized bed. The holding means for holding the workpiece in a process involving progressively feeding the workpiece may with advantage be adapted to traverse the workpiece past the induct or in the fluidized bed. Preferably there may be provided, outside the fluidized bed in the direction of motion behind the first inductor, a second inductor in heating position to the workpiece surfaces that are to be coated. In a convenient embodiment of apparatus according to the invention for coating surfaces on axially symmetrical workpieces such as circular knives, the holding means may rotate the workpiece about its symmetry axis.

In yet another useful modification of the proposed apparatus the holding means may be attached to a vertically movable slide and an inductor coil may be attached to the slide by its feeding conductors, means being provided for slidably moving the slide from a lower position in which the inductor coil and the region of the workpiece surface that is to be coated are below the surface level of the fluidized bed into an upper position in which both are outside the level of the fluidized bed. Conveniently the inductor coil may embrace the tank containing the fluidized bed and may thus always remain outside the fluidized bed.

The invention will be more particularly described with reference to the drawings which illustrate embodiments of apparatus according to the invention.

FIGS. 1 and 2 are two schematic elevations of apparatus for applying a coating to peripheral surface regions of an axially symmetrical workpiece.

FIG. 3 shows a further embodiment of the invention.

In the illustrated embodiment of FIGS. 1 and 2 the workpiece is a circular knife 1 which is to receive a coating on both sides of its cutting edge 2. Circular knife 1 is rotably mounted in a convention chucking device generally indicated by 3 and adapted to be rotated about a horizontal axis in the direction indicated by an arrow 4. Part of the circumference of the circular knife dips into a tank 5 which is provided with a perforated bottom 6. The tank contains a fluidized solids bed 7 in which the coating material that is to be applied to the edge 2 of the blade is kept in suspension in an ascending current of a fluidizing gas which enters through the perforated bottom 6. A suitable fluidizing gas may be Argon. Located inside fluidized bed 7 is an inductor provided with a heating conductor loop 8 fed with a high frequency current. The conductor loop embraces a portion of the cutting edge 2 of the circular knife 1. A second inductor comprising a similar heating conductor loop 9 is located outside the fluidized bed in a corresponding position in relation to the cutting edge 2 of the circular knife.

The chucking device 3 rotates circular knife 1 in the direction indicated by arrow 4 so that the cutting edge of knife 1 passes between heating conductors 8 and 9. By switching on a high frequency current which flows through heating conductor 8, cutting edge 2 of circular knife 1 can be inductively heated to a temperature which is slightly above the melting temperature of the coating material. The powder suspended in bed 7 cakes to the inductively heated part of circular knife 1 and then fuses to this region progressively from the surface of the base material to the outside. The regions of circular knife I to which the powdered coating material has been applied in this fluidized bed are now moved out of bed 7 by the rotation of circular knife I in the direction of arrow 4 and passed through heating conductor 9 which is likewise fed with the high frequency current and these regions are thus reheated and thereby homogenized. Preferably conductors 9 are arranged so that the gas exiting from tank 5 surrounds conductor 9 as it inductively reheats cutting edge 2. The thickness of the coating can be varied by adjusting the speed of rotation of the circular knife. Further the above steps can be repeated as many times as desired to coat the workpiece to any desired thickness while still obtaining an excellent bond between the two metals.

In FIG. 3 the end portion 11 of a bolt-shaped workpiece which is to be coated dips into a cylindrical tank 12 in which the powder of coating material is maintained in a fluidized state 13 in the same fashion as in FIGS. 1 and 2. By means of a collet 14 the workpiece is attached to a slide 15 which is vertically movable in a machine column indicated at 16. Slide 15 also carries feeder conductors 17 of a multiple coil inductor 18. Thus, inductor l8 embraces cylindrical tank 12 containing the fluidized bed and extends the length of the surface region 1] on the workpiece 10 that is to be coated.

For applying the coating to the workpiece 10 power is switched on when the slide 15 and the inductor coil are in the position shown in FIG. 3, in which the portions of the workpiece 10 that are to be coated are surface heated. Consequently the particles of coating material in the fluidized bed cake and fuse to the inductively heated surface in a manner analogous to that described with reference to FIGS. 1 and 2. At the end of a specified time the slide is raised into an upper position in which both the workpiece l0 and the induction coil 18 are outside the fluidized bed so that the regions of the workpiece 10 that are to be coated can be further heated for a given period of time during which the coating applied in the fluidized bed can homogenize. As in the embodiment of FIGS. 1 and 2 these steps can be repeated to obtain any desired thickness.

Many changes and modifications in the above embodiments of the invention can of course be made without departing from the scope of the invention. Accordingly that scope is intended to be limited only by the scope of the appended claims.

What is claimed is:

I. A method of applying a coating of metallic material to specified metal regions on a base material of a different metal comprising the steps of:

immersing at least the metal surface regions of the workpiece that are to be coated in a fluidized bed containing particles of the coating metallic material,

providing an ascending current of gas in said fluidized bed so that said coating particles are suspended,

inductively heating in the fluidized bed a surface layer of the workpiece in the regions that are to be coated in the fluidized bed so that said suspended material from the fluidized bed is deposited on said inductively heated regions and inductively reheating the coated material outside the fluidized bed after deposition.

2. A method according to claim 1, wherein the gas is an inert gas.

3. A method according to claim 2, which is characterized in that the inert gas is a noble gas.

4. A method according to claim 1, including the further step of surrounding the regions to be coated with said fluidizing gas of the fluidized bed during the second inductive heating.

5. A method according to claim 1 wherein said step of inductively heating outside said bed includes the step of moving at least the surface regions that are to be coated through an inductive energy transducer outside the fluidized bed.

6. A method according to claim 1 wherein said step of inductively heating includes the step of moving at least the region of the workpiece that is to be coated through an inductive energy transducer inside the fluidized bed.

7. A method according to claim 1 including the steps of withdrawing an inductive energy transducer which has caused the powder to be deposited on the surfaces in the fluidized bed from the fluidized bed together with the workpiece and thereafter reheating the surfaces that are to be coated with that transducer outside said bed.

8. A method according to claim 1 including repeating the above steps until a desired thickness of coating is produced 

1. A METHOD OF APPLYING A COATING OF METALLIC MATERIAL TO SPECIFIED METAL REGIONS ON A BASE MATERIAL OF A DIFFERENT METAL COMPRISING THE STEPS OF: IMMERSING AT LEAST THE METAL SURFACE REGIONS OF THE WORKPIECE THAT ARE TO BE COATED IN A FLUIDIZED BED CONTAINING PARTICLES OF THE COATING METALLIC MATERIAL, PROVIDING AN ASCENDING CURRENT OF GAS IN SAID FLUIDIZED BED SO THAT SAID COATING PARTICLES ARE SUSPENDED, INDUCTIVELY HEATING IN THE FLUIDIZED BED A SURFACE LAYER OF THE WORKPIECE IN THE REGIONS THAT ARE TO BE COATED IN THE FLUIDIZED BED SO THAT SAID SUSPENDED MATERIAL FROM THE FLUIDIZED BED IS DEPOSITED ON SAID INDUCTIVELY HEATED REGIONS AND INDUCTIVELY REHEATING THE COATED MATERIAL OUTSIDE THE FLUIDIZED BED AFTER DEPOSITION.
 2. A method according to claim 1, wherein The gas is an inert gas.
 3. A method according to claim 2, which is characterized in that the inert gas is a noble gas.
 4. A method according to claim 1, including the further step of surrounding the regions to be coated with said fluidizing gas of the fluidized bed during the second inductive heating.
 5. A method according to claim 1 wherein said step of inductively heating outside said bed includes the step of moving at least the surface regions that are to be coated through an inductive energy transducer outside the fluidized bed.
 6. A method according to claim 1 wherein said step of inductively heating includes the step of moving at least the region of the workpiece that is to be coated through an inductive energy transducer inside the fluidized bed.
 7. A method according to claim 1 including the steps of withdrawing an inductive energy transducer which has caused the powder to be deposited on the surfaces in the fluidized bed from the fluidized bed together with the workpiece and thereafter reheating the surfaces that are to be coated with that transducer outside said bed.
 8. A method according to claim 1 including repeating the above steps until a desired thickness of coating is produced. 